Cervical cancer is the leading female cancer in Uganda. Many women are diagnosed with late-stage disease, and 80% of women die within 5 years of diagnosis, making primary prevention critical. HPV is the principal cause of cervical cancer, making vaccination the single most important primary preventive measure. The national HPV vaccination program in Uganda began in November 2015 and focuses solely on preteen/adolescent girls. Two strategies have been adopted for the multi-dose series: 1) school-based and 2) community-based. However, in Kampala, only 29% of girls receive both needed doses. Reasons for under vaccination include school absenteeism on special vaccination days for those receiving vaccination as part of a school program, failing to remember to come to a health facility for a needed dose for those being vaccinated in the community, and lack of knowledge regarding HPV and the vaccines including vaccine misperceptions. While research regarding the use of text message vaccine reminders is strong in the U.S., their use has not yet been demonstrated in a preteen/adolescent population in Sub-Saharan African or other low- and middle- income countries (LMICs). According to the World Bank, currently 89.9% of urban households in Uganda have a cell phone. This study will take place at three health centres and their affiliated schools and community immunization centers overseen by the Kampala Capital City Authority (KCCA) as well as at the Makerere/Mulago/Columbia Adolescent Health Clinic, also in Kampala. While text messages can be used in populations with low literacy, families can opt to receive automated phone call reminders instead. R21: Aim 1: Identify desired HPV vaccine text message reminder content (and parallel automated phone reminders) using key informant interviews We will conduct formative research using key informant interviews with stakeholders at each site as well as policy makers. Aim 2: Develop and pretest HPV vaccine reminders with target population We will share prototypes of the designed messages with families to identify issues with clarity, tone, and persuasiveness. Aim 3: Pilot assess the impact of vaccine reminders on HPV vaccination We will randomize caregivers of preteens/adolescents at one KCCA site and the adolescent clinic, stratified by site, language and HPV vaccine dose needed (initiation vs. completion). Feasibility milestones will include reach, effect size determination and implementation measures. R33: Aim 4: Conduct a full-scale randomized-control trial to assess the impact of text message reminders on HPV vaccination We will conduct a full-scale RCT assessing the impact of the HPV vaccine text message reminders. The main outcome will be timeliness of vaccination. We will also collect process/feasibility measures. This project, if successful, will provide an important foundation not only for the use of HPV vaccine text message reminders in Uganda but also for other childhood and adolescent vaccinations in Uganda and in other LMICs.